This application is based on JP-A-2005-156949 filed on May 30, 2005, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a temperature detector for measuring the surface temperature of a temperature-measured object, such as a fixing roller or the like, in an image forming apparatus, such as a copier, a printer, a facsimile, or the like, and also to a fixing device including this temperature detector.
2. Description of the Prior Art
Conventionally, in an image forming apparatus that forms a toner image on paper to thereby obtain a visible image, for example, as shown in FIG. 6, a toner image formed on paper P is fixed by having the paper P pass through a pressure-contact portion between a fixing roller 52 (heating roller) having a halogen lamp 51 built therein as a heat source and a pressure roller 53, which are both included in a fixing part 50 (that is, fixing device), and then applying heat and pressure to the toner on the paper P. An arrow with a solid line denotes the conveyance direction of the paper P.
To obtain a favorable toner image on the paper P in the fixing processing, it is required to maintain the fixing roller 52 at a previously set adequate temperature in the fixing processing. Thus, as shown in FIG. 6, with a temperature detector 54 placed in contact with the surface of the fixing roller 52, ON-OFF control of the halogen lamp 51 is performed based on the output of the temperature detector 54.
The conventional temperature detector 54 that detects the temperature of the fixing roller 52 has, as shown in FIG. 7, a temperature detection part 55, such as a thermistor or the like, sandwiched between polyimide sheets 56 and 57 which are provided in an orange color as protection members therefor. Then, the temperature detection part 55 is protected, by the polyimide sheet 56 placed in contact with the surface of the fixing roller 52, from friction with the fixing roller 52.
Disclosed and suggested in technical literature as a reference for a temperature detector is a temperature detection unit in which a metal piece is arranged between a protection member of a Teflon (registered trademark) sheet in contact with a fixing roller and a temperature detection element and then an insulating heat-resistant sheet is disposed between the metal piece and the temperature detection element (for example, see patent publication 1).
[Patent Publication 1] JP-A-H11231715
The conventional temperature detector 54 definitely can protect the temperature detection part 55, by the polyimide sheet 56, from the friction with the fixing roller 52, and also can detect the surface temperature of the fixing roller 52 as a temperature-measured object.
With the temperature detection unit disclosed in patent publication 1, the temperature of the fixing roller can be detected without causing temperature misdetection by the temperature detection element due to insulation failure. Moreover, since the protection member in contact with the fixing roller is a Teflon (registered trademark) sheet, adhesion of the toner, which has adhered to the fixing roller, to the protection member can be reduced.
However, in the conventional temperature detector 54, the polyimide sheet 56 protecting the temperature detection part 55 has low heat conductivity and exhibits low heat absorbing performance (heat collection effect ) for radiant heat due to its surface colored in orange; therefore, heat is not efficiently conducted from the fixing roller 52 to the temperature detection part 55, thus resulting in low responsiveness of the temperature detection part 55 in temperature detection. Moreover, as means for improving the responsiveness of the temperature detection part 55 in temperature detection, it is possible to provide the polyimide sheet 56 with a thin thickness, although this results in decreased endurance of the polyimide sheet 56. Furthermore, the conventional temperature detector 54 has a risk that the toner, which has adhered to the fixing roller 52, adheres to the polyimide sheet 56 thereby causing misdetection of the surface temperature of the fixing roller 52.
Further, the temperature detection unit disclosed in patent publication 1 has the protection member, the metal piece, and the insulating heat-resistant sheet that are only stacked one on the other, thus having room for improvement in the responsiveness of the fixing roller in temperature detection.